This application claims the benefit of the Korean Application Nos. P2002-7503 and P2002-7510 filed on Feb. 8, 2002, which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an induction motor, and more particularly, to an outer rotor type induction motor having a rotor outside a stator.
2. Discussion of the Related Art
Generally, a motor converts an electric energy into a mechanical energy so as to provide a rotatory power. Motors are mainly divided into AC motors and DC motors, in which an induction motor is a kind of the AC motors.
The induction motors are divided again into an inner rotor type induction motor and an outer rotor type induction motor in accordance with relative positions of rotors and stators. The inner rotor type induction motor is generally applied to a washing machine or the like, and includes the rotor inside the stator.
As the rotor of the inner rotor type induction motor rotates through an inside of the stator, a radius of the rotor is limited so as to produce a less torque per unit volume as well as reduce its utilization of the inner space. Lately, proposed is an induction motor enabling to increase the torque per the same volume in a manner that the rotor is installed outside the stator as well as utilize the inner space of the stator for other usage. Such an induction motor is called an outer rotor type induction motor.
A general structure of the outer rotor type induction motor is explained briefly as follows.
FIG. 1 illustrates a schematic cross-sectional view of a general outer rotor type induction motor.
Referring to FIG. 1, an outer rotor type induction motor includes a rotor housing 10 with which a driving shaft 60 is coupled so as to penetrate a center of the rotor housing 10, a rotor conductor 20 installed at an inner circumference face of the rotor housing 10 so as to constitute a connected circuit, a stator core 30 fixed to a frame 50 so as to maintain a predetermined slit with the rotor conductor 20 inside the rotor housing 10, and a coil 40 installed at the stator core 30 so as to form a rotatory magnetic field by receiving an AC electric power.
In this case, the driving shaft 60 is coupled with the rotor housing 10 through an insertion hole 11 of the rotor housing 10, and then penetrates a center of the stator core 30 so as to be supported to rotate by the frame 50.
Operation of the above-constituted induction motor is schematically explained as follows. The rotatory magnetic field generated from the coil 40 inter-reacts with a current induced on the rotor conductor 20, thereby generating a torque revolving the rotor conductor 20 in accordance with Fleming""s left hand rule.
Yet, in spite of the above-explained advantage, the outer rotor type induction motor has the following disadvantages or problems so as to fail to be used widely.
First, in induction motors including the outer rotor type induction motor, copper loss due to an electric resistance of the coil 40 and core loss due to leakage flux of the stator core 30 are inevitable. The copper and core losses bring about heat considerably. In this case, a temperature inside the induction motor increases so as to increase a resistance of the coil 40, thereby increasing a power loss. Specifically, if the temperature inside the induction motor is higher than that of an insulation level of the coil 40, an insulating film formed on a surface of the coil 40 is broken to reduce an endurance of the induction motor severely.
Such a problem becomes severer in the outer rotor type induction motor. As a load torque per volume of the outer rotor type induction motor works more greatly than that of the inner rotor type induction motor, such a load torque results in the temperature increase of the coil 40 directly.
Second, the outer rotor type induction motor has difficulty or weakness in winding the coil 40 on the stator core 30 automatically, whereby automatic mass-production is unavailable so as to increase a product cost.
Generally, there are various methods of winding the coil on the stator core. For instance, an inserting method is carried out by inserting the coil, which is wound previously using a winding machine, into a stator slot automatically. And, a direct winding method is carried out by winding the coil on the stator slot directly. The inserting method us applied to the inner rotor type induction motor. Despite its product cost higher than that of the direct winding method, the inserting method enables the automation so as to be applied to the mass production.
Yet, in order to apply the inserting method to the outer rotor type induction motor, new instruments including a winding machine and the like are required. Hence, the direct winding method is mainly applied to the outer rotor type induction motor. This is because the position and shape of the stator slot of the outer rotor type induction motor are absolutely different from those of the inner rotor type induction motor.
Even if the direct winding method is applied to the outer rotor type induction motor, the automation is impossible.
Specifically, the outer rotor type induction motor, as shown in FIG. 2, needs a plurality of poles in order to attain a rotatory power. A count of the poles depends on an arrangement form of the coil. Generally, the widely used coil arrangement form constitutes eight poles using forty-eight stator slots 31.
Hence, six stator slots 31 are allocated to each of the poles, and the coil is suitably wound on the six stator slots. In this case, the coil is divided into a main winding MC as an operating winding and a supplementary winding SC as a starting winding. For convenience of explanation, random numerals are given to the main winding MC, supplementary winding SC, and stator slot 31 like FIG. 2. First, a first main winding MC1 is wound through most outer stator slots 31a and 31f among the stator slots, and then a second main winding MC2 is wound through another stator slots 31b and 31e. And, first and second supplementary windings SC1 and SC2 are wound through most inner stator slots 31c and 31d among the stator slots, respectively. In this case, third and fourth supplementary windings SC3 and SC4 are wound together through the stator slots 31b and 31e through which the second main winding MC2 is wound, respectively.
In this case, cross-sectional areas(area of a space in which the coil is wound) of the stator slots 31 are equal to each other, there is difficulty in winding the coil automatically. As the stator slot on which another coil is wound exists between the stator lots where a random coil is wound, spaces in which the coils are wound are overlapped with each other so as to bring about a competition between the coils. For instance, four stator slots 31b, 31c, 31d, and 31e are formed between the most outer stator slots 31a and 31f on which the first main winding MC1 is wound. In this case, the first main winding MC1 comes into competition with the second main winding MC2 and first to fourth supplementary windings SC1 to SC4 wound on the rest stator slots 31b, 31c, 31d, and 31e in the same space.
Unfortunately, it is substantially impossible to wind the coil automatically to bring about an automated mass production, thereby increasing a product cost. Besides, it is able to prevent the coils from competing each other in the winding space by securing the cross-sectional area of the stator slot 31 sufficiently, whereby a size of the stator core has to be increased.
Accordingly, the present invention is directed to an outer rotor type induction motor that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an outer rotor type induction motor enabling to improve a reliance and an endurance of a product as well as reduce its power consumption by cooling a coil smoothly.
Another object of the present invention is to provide an outer rotor type induction motor enabling an automated mass production by minimizing an reciprocally overlapped space in coil-wound spaces.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an outer rotor type induction motor includes a driving shaft, a stator core fixed to a frame and having a plurality of stator slots so that the driving shaft penetrates a center of the stator core, a coil wound on the stator slots so as to form a rotatory magnetic field, a rotor housing installed outside the stator core so as to maintain a predetermined slit with the stator core wherein the driving shaft is coupled through a bottom center of the rotor housing, a rotor conductor coupled with an inner circumference face of the rotor housing so as to generate a torque by the rotatory magnetic field of the coil, and a plurality of upper blades installed at an upper end of the rotor housing so as to leave a predetermined interval therebetween wherein an external air is forcibly sucked in to cool the coil when the rotor housing revolves.
Therefore, the present invention makes the coil cooled by the air circulating forcibly by the upper blade, thereby enabling to overcome the decrease of the endurance and the increase of power consumption due to the temperature increase of the coil simultaneously.
In another aspect of the present invention, an outer rotor type induction motor includes a driving shaft, a stator core fixed to a frame so that a center of the stator core is penetrated by the driving shaft, a plurality of stator slots formed at the stator core so as to be in parallel with the driving shaft and differing in depth toward the driving shaft, a coil wound directly on the stator slots as a distributed winding so as to form a rotatory magnetic field, the coil comprising main and supplementary windings, a rotor housing installed outside the stator core so as to maintain a predetermined slit with the stator core wherein the driving shaft is coupled through a bottom center of the rotor housing, and a rotor conductor coupled with an inner circumference face of the rotor housing so as to generate a torque by the rotatory magnetic field of the coil.
Therefore, the present invention secures sufficiently the space failing to be overlapped between the coils with a depth difference of the stator slots, thereby enabling to wind the coil using a winding machine.
In a further aspect of the present invention, an outer rotor type induction motor includes a driving shaft, a stator core fixed to a frame so that a center of the stator core is penetrated by the driving shaft, a plurality of stator slots formed at the stator core so as to be in parallel with the driving shaft and differing in depth toward the driving shaft, a coil wound directly on the stator slots as a distributed winding so as to form a rotatory magnetic field, the coil comprising main and supplementary windings, a rotor housing installed outside the stator core so as to maintain a predetermined slit with the stator core wherein the driving shaft is coupled through a bottom center of the rotor housing, a rotor conductor coupled with an inner circumference face of the rotor housing so as to generate a torque by the rotatory magnetic field of the coil, and a plurality of upper blades installed at an upper end of the rotor housing with a predetermined interval each other so that an external air is forcibly sucked in to cool the coil when the rotor housing revolves.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.